J. Biol. Chem., Vol. 262, Issue 18, 8626-8630, 06, 1987
Development of opiate receptors and GTP-binding regulatory proteins in neonatal rat brain
G Milligan, RA Streaty, P Gierschik, AM Spiegel and WA Klee
The mu and delta opiate receptors present in rat brain were measured
independently during postnatal development. The numbers of delta receptors
were almost undetectable at birth and increased substantially during the
first few weeks, whereas the numbers of mu receptors remained relatively
constant. Activation of either of these receptors caused inhibition of
adenylate cyclase, but inhibition coupled to mu receptors was much smaller
than that associated with delta receptors at all ages. Attempts to use
pertussis toxin-catalyzed ADP-ribosylation as an assay for the GTP-binding
proteins Ni and No were hampered by the development of an NADase with age.
However, specific antibodies directed against the alpha subunits of Ni or
No allowed separate quantitation of these transducer proteins. Both
increased with age. No is present at levels at least 5-fold higher than Ni
in the adult rat brain. The N proteins are in vast excess over receptors
and as such are unlikely to be limiting factors in receptor function. The
data further suggest that the number of opiate receptors present throughout
neonatal development is in excess over that required for optimal function.
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